This invention relates to a method of sensing abnormalities of a weft detecting device employed in a loom.
Ordinarily, the position in which a weft is detected by a weft feeler, namely the crank angle phase during one revolution of a loom, is approximately constant for each revolution even though there may be some degree of variance, the crank phase angle being limited to within a certain crank angle range. Accordingly, the effect of extaneous signals other than weft signals for a fabric or the like can be excluded to enhance reliability by restricting, to a suitable range which includes the aforementioned crank angle range, the range over which the weft feeler performs the operation of detecting weft insertion errors. This relationship is expressed by the diagram of FIG. 1. Specifically, no detection signal S.sub.2 indicative of a weft insertion error is generated when a weft detection signal S.sub.1 is detected in a weft detection angle range A.sub.1 where the range of the crank angle is constant, but the detection signal S.sub.2 indicative of a weft insertion error is generated when no weft detection signal S.sub.1 is detected in the range A.sub.1. Thus, reliability is enhanced since the detection operation is not performed even if extraneous signals occur outside of the weft detection angle range A.sub.1.
It should be noted, however, that a large quantity of extraneous signals S.sub.o (which are taken as being pulsed signals similar to the weft detection signals S.sub.1) are generated if flies or yarn waste attach to the detection portion of the weft feeler, if the mounting of the detection portion loosens, if a wire is about to break and makes intermittent contact, or if extraneous noise is received. If these extraneous signals S.sub.o occur also in the weft detection angle range A.sub.1, as shown in FIG. 2, a weft insertion error cannot be detected owing to the signal S.sub.o, even though the weft (the weft detection signals S.sub.1) is not detected. The disadvantageous result is that a void appears in the woven fabric.